In the mining industry, depletion of high-grade ore invariably results in development of methods to utilize ore containing impurities and lower concentrations of the desired mineral. Low-grade, impure ore is concentrated and purified to meet commercial standards, through various processes collectively referred to in the industry as "beneficiation". An overriding concern, of course, is efficiency. Any such method must be cost-effective and competitive with the recovery of naturally high-grade ores.
The mining and purification of iron ore exemplifies this wide-spread phenomenon. Typically, in one common beneficiation process, hematite, magnetite, goethite, or martite-type ore is finely ground to liberate undesirable mineral impurities referred to as "gangue". (Gangue, as found in most iron ore deposits, is a siliceous material such as quartz, clay, etc. and will hereinafter be referred to as silicates, the presence of which adversely affect steel quality and the amount of slag by-product generated in its manufacture.)
The ore or a concentrate thereof is then mixed with water to form a pulp, which is transferred to a large flotation cell equipped with an agitator. Air is introduced into and passed through the pulp. A frothing agent, usually a low molecular weight alcohol, may be used. The froth formed is skimmed-off or allowed to overflow. Undesired silicates float away with the froth, leaving a purer ore concentrate for further processing.
In carrying out the flotation step, a collector agent capable of silicate chelation is added to the pulp. Silicates wetted by the collector agent are hydrophobic and have a surface active affinity for the froth formed. Separation is achieved as the chelated silicates float with the froth to the top of the flotation cell.
The search for an efficient, effective collector agent meeting the requirements stated above has been an ongoing concern in the art. A host of such agents have been developed over the years. While many have been used with some success, most have been limited by poor water dispersability and selectivity, high cost, and general ineffectiveness.
One approach, which has been used with some success, involves the use of various cationic collector agents, including ether amines having the general structural formula EQU R--O--(CH.sub.2).sub.n NH.sub.2
where the R--O-- portion is derived from a mixture of linear and branched C.sub.8 and C.sub.10 alcohols. Other ether amines have been prepared from higher molecular weight linear and branched alcohols. Regardless, as a matter of practicality and formulation, many such ether amines, as well as their amine analogues, are at least partially neutralized (approximately 30%) with acetic acid, solely to improve water dispersability. (See U.S. Pat. Nos. 4,319,987 and 4,422,928).
Other cationic collector agents used in ore flotation processes include fatty amines, fatty beta-amines, various ether diamines (See U.S. Pat. Nos. 3,363,758 and 3,404,165) and, more recently, blends of alkyl amines/mono ether amines (See U.S. Pat. No. 4,168,227). Again, neutralization (acetic acid) frequently is necessary to effect a satisfactory degree of water dispersability.
However, the prior art has associated with it a number of significant problems and deficiencies. Most are related to inadequate silicate separation and result from the collector agents currently used.
A major problem is that collector agents of the prior art tend to have low selectively. They chelate iron ore, in addition to silicates, removing the iron with the froth. Loss of iron in this manner decreases cost-effectiveness and makes the overall beneficiation process less competitive. Furthermore, iron is entrained in the froth generated, overflows of which result in additional loss of iron.
To counter low selectivity, flotation depressants are sometimes used to inhibit iron chelation and prevent removal with silicate impurities. Starch-type and synthetic depressants enhance iron recovery, but their use is cost-prohibitive.
Collector agents of the prior art also act as emulsifiers, in that they stabilize the froth generated. As a result receiving troughs, pumping reservoirs, and other components experience overflow. Because the froth does not collapse within a reasonable amount of time, severe material handling problems arise.
Transfer of the froth between a series of flotation cells or to other components of the beneficiation process becomes problematical as standard pumping mechanisms are designed to move liquid rather than a gaseous froth. Magnetic separators used to further process magnetite-type ore are also adversely affected, as are tailing thickener operations. Inefficiencies of this nature reduce production rates and increase the overall costs of the beneficiation process.
The aforementioned overflow problems adversely effect plant safety and maintenance. In some instances, redesign of the flotation process is necessary also at great expense.
To compensate for the deficiencies of the prior art, defoamers and collector agents are used in the flotation process. Typically, materials such as silicones, fuel oils or kerosene, or fatty alcohols are added to control the amount of froth produced. The real cost of the collector agent is significantly higher when the price of a defoamer is considered. In such cases, the flotation process must be redesigned to incorporate extra pumping and monitoring components to accommodate use of a defoamer. Furthermore, some defoamers, such as those mentioned above, are odiferous and present numerous worker safety problems.
To circumvent some of the aforementioned concerns, less frothing agent may be used in certain circumstances to decrease the amount of froth generated. However, as a means of compensation, more collector agent is usually employed. The problem then reverts to low selectively and loss of iron ore, raising the overall production cost.
In summary, a considerable number of drawbacks and problems exist in the art relating to the use of collector agents in ore flotation processes. There is a need for an improved flotation aid composition.